The present invention relates to a method and apparatus for feeding sheets from a stack. The invention is particularly useful for feeding sheets of fabric from a stack or pile, and is therefore described below with respect to this application.
The feeding of paper, cardboard and similar sheets is relatively simple, and many such feeding devices have been developed and are in widespread use. The feeding of fabrics and similar types of limp and/or porous materials is considerably more difficult because of the limpness and porosity of such materials, in addition to their softness, roughness, compressibility, surface friction or adhesion, and the like. The foregoing properties of such materials introduce many problems which are difficult to overcome in an automatic handling system. Thus, the limpness and softness of these materials cause contacting surfaces to intermesh, making them difficult to separate; their limpness also makes lifting difficult; their roughness causes the underlying sheet to be carried with the upper sheet when moved transversely of the stack or pile; the threads at the edges of the adjacent sheets often are entangled and not aligned. Vacuum devices for lifting such sheets are usually not effective because of the porosity of the sheets. Adhesives have also so far been found ineffective, and are usually not desired because of the possibility of marking or damaging the sheets. A number of air-jet devices have been designed for this purpose, in which the air-jets produce a lift or flutter of the topmost sheet for separating it. Examples of the latter type devices are illustrated in U.S.A. Pat. Nos. 3,877,695, 3,796,455, 3,738,645, 3,647,202, 3,596,900, 3,539,177, 3,168,308 and 3,168,307; but even these air-type devices have still not been found entirely satisfactory.